Ya Cheng

Investigation of photoreaction mechanism of photosensitive glass by femtosecond laser

A high-intensity femtosecond (fs) laser can fabricate complicated three-dimensional microstructures inside photosensitive glass with high spatial resolution. In this work, the mechanism of the photoreaction of the photosensitive glass to the infrared fs laser is investigated. We examine the photoinduced electron excitation process on the basis of the determination of the critical dose and a change of the optical-absorption spectrum after the fs laser irradiation. The photoreaction mechanism is discussed in comparison with the case of an ultraviolet nanosecond laser irradiation. Finally, the successive interband electron excitation through defect levels by multiphoton absorption is proposed.

3D microfabrication in photosensitive glass by femtosecond laser

We describe a true three dimensional (3D) microfabrication of photosensitive glass by applying a femtosecond (fs) laser which works at fundamental wavelength. First, designed microstructure was written into the glass sample by a tightly focused fs laser beam (wavelength 775nm, pulse width 145±5fs, repetition rate 1kHz); next, this sample underwent a programmed heat treatment; finally it was immersed into 10% hydrofluoric (HF) acid to take an ultrasonic bath. By this approach, true 3D microstructures with embedded microchannels and microcells are directly formed inside the glass matrix, without extra bonding or adhering procedures in those planar fabrication techniques. Such an approach combines the advantages of high precision in laser microfabrication and cost-effectiveness in chemical processing, therefore, could be a promising tool in futuristic manufacture of micro total analysis systems (μ-TAS) and micro fluidic devices.

3D integration of microoptics and microfluidics in glass using femtosecond laser direct writing

We describe the fabrication of 3D microoptics and microfluidics embedded in glass using femtosecond laser direct writing. By integrating the microoptics and the microfluidics, microfluidic dye lasers three-dimensionally embedded in glass have been fabricated for the first time. By pumping the microfluidic laser, in which the microfluidic chamber was filled with laser dye rhodamine 6G dissolved in ethanol, by a frequency-doubled Nd:yttrium aluminum garnet laser, lasing action was confirmed by analyzing the emission spectra at different pumping powers. In addition, by arranging two microfluidic chambers serially in the glass, we built a microfluidic twin-laser which produces an array of two simultaneous laser emissions with one pumping laser. The integration of microoptics and microfluidic in a single glass chip paves the way toward the automatic fabrication of biophotonic chips.

Three-dimensional micro-optical components embedded in Foturan glass by a femtosecond laser

Three-dimensional (3D) microoptical components are embedded in a photosensitive glass Foturan by a femtosecond (fs) laser. This process includes mainly three steps: (1) direct writing of latent images in the sample by the tightly focused fs laser beam; (2) baking of the sample in a programmable furnace for the formation of modified regions; and (3) etching of the sample in a 10% diluted solution of hydrofluoric acid for the selective removal of the modified regions. After this process, hollow internal structures are formed, which act as a mirror and a beam splitter. Furthermore, we find that postannealing smoothes the surfaces of the fabricated hollow structures, resulting in the great improvement of the optical properties. We examine the optical properties of the structured components using a He-Ne laser beam, and measure the optical losses at 1.55 μm wavelength.

THREE-DIMENSIONAL MICRO AND NANOCHIPS FABRICATED BY FEMTOSEDOND LASER FOR BIOMEDICAL APPLICATIONS

. Abstract. Three-dimensional (3D) micromachining of photosensitive glass is demonstrated by a photochemical reaction using femtosecond (fs) laser for lab-on-a-chip application. True 3D hollow microstructures embedded in the glass are fabricated by fs laser direct writing followed by heat treatment and successive wet etching. The modification mechanism of the photosensitive glass by the fs laser and advantage of this process are discussed. Various microcomponents for the lab-on-a-chip devices such as microfluidics, microvalves, microoptics, microlasers, etc. are fabricated by using this technique and their performance is examined.

Femtosecond laser microfabrication of 3D structures in Foturan glass

Currently, high throughput manufacture of Lab-on-a-chip devices integrated with both microoptics and microfluidics faces serious challenges, including assembly and packaging. Because of their different physical properties and functions, the optical and the fluidic elements are often first separately fabricated on different substrates, and then assembled into a single Lab-on-a-chip device. The alignment between the microoptical and microfluidic components requires micron-scale precision. To overcome this difficulty, we recently developed a novel laser microfabrication technique to form 3D hollow structures buried in a photosensitive glass - Foturan. The formation of both the optical and the fluidic structures were completed in a unified fabrication process. The technique is based on femtosecond laser direct writing followed by post-baking and successive chemical etching, completely eliminating the assembling procedures such as alignment, fixation, stacking, and bonding that are inherent in traditional 3D microprocessing techniques. In this paper, we describe the fabrication of a broad variety of hollow structures in Foturan glass, and the integration of these structures to build functional micro-devices. Furthermore, we will discuss how to control the fabrication resolution in three dimensions by developing novel beam focusing schemes to generate isotropic focal spot shapes inside the transparent materials.

Advanced irradiation methods of femtosecond laser for embedded microfabrication of transparent materials

Large scale, true three dimensional (3D) microchannel structures have been fabricated in photosensitive glass by femtosecond (fs) laser. In general, the microchannel fabricated inside glass by scanning focal spot of fs laser perpendicularly to the laser propagation direction gets an elliptical shape with a large aspect ratio of its cross section, which is undesirable to most of micro total analysis systems (μ-TAS) or micro fluidic devices. In this paper, we describe how to improve the aspect ratio of the fabricated microchannel by using advanced irradiation methods of fs laser.

Three-dimensional patterning in transparent materials with spatiotemporally focused femtosecond laser pulses

According to specific configurations, three-dimensional (3D) patterning involves both 3D bioimaging and laser micromachining. Recent advances in bioimaging have witnessed strong interests in the exploration of novel microscopy methods capable of dynamic imaging of living organisms with high resolution, and large field of view (FOV). For most, applications of bioimaging should be limited by the tradeoff between the speed, resolution, and FOV in common techniques, e.g., confocal laser scanning microscopy and two-photon microscopy. However, a recently proposed temporal focusing (TF) technique, based on spatio/temporal shaping of femtosecond laser pulses, enables depth-resolved bioimaging in a wide-field illumination. This lecture firstly provides a glimpse into the state-of-the-art progress of temporal focusing for bioimaging applications. Then we reveal a bizarre point spread function (PSF) of the temporal focusing system, both experimentally and theoretically. It can be expected that this newly emerged technique will exhibited new advances in not only 3D nonlinear bioimaging but also femtosecond laser micromachining in the future.

3D microstructuring of glass by femtosecond laser direct-writing for micro-TAS application

Three-dimensional (3-D) microstructuring of photosensitive glass is demonstrated by using femtosecond (fs) laser for Lab-on-chip, in other words, micro total analysis system (μ-TAS), application. The fs laser direct-write process followed by a thermal treatment and chemical etching in a HF aqueous solution produces true 3-D hollow microstructures embedded in the photosensitive glass. This technique is applied for manufacturing a microfluidic structure inside the glass. Mixing of two kinds of aqueous solutions is demonstrated in the fabricated structure. A freely movable microplate is also fabricated inside glass to control a stream of reagents in the microfluidics. In the meanwhile, this technique is applied for integrating microoptics like micromirror and micro beam splitter in the glass chip for optical analysis of reactants produced in the microfluidics. This paper also discusses the mechanism of fs laser and photosensitive glass interaction.

Advanced laser processing of glass materials

Three kinds of advanced technologies using lasers for glass microprocessing are reviewed. Simultaneous irradiation of vacuum ultraviolet (VUV) laser beam, which possesses extremely small laser fluence, with ultraviolet (UV) laser achieves enhanced high surface and edge quality ablation in fused silica and other hard materials with little debris deposition as well as high-speed and high-efficiency refractive index modification of fused silica (VUV-UV multiwavelength excitation processing). Metal plasma generated by the laser beam effectively assists high-quality ablation of transparent materials, resulting in surface microstructuring, high-speed holes drilling, crack-free marking, color marking, painting and metal interconnection for the various kinds of glass materials (laser-induced plasma-assisted ablation (LIPAA)). In the meanwhile, a nature of multiphoton absorption of femtosecond laser by transparent materials realizes fabrication of true three-dimensional microstructures embedded in photosensitive glass.